Effect of isomeric oxydiphenylene diamine on the water sorption behavior of high temperature polyimide thin films

The effects of isomeric oxydiphenylene diamines (ODA), 3,4′ODA and 4,4′ODA, on the water sorption behavior in pyromellitic dianhydride (PMDA)-ODA, biphenyltetracarboxylic dianhydride (BPDA)-ODA, 3,3′,4,4′-benzo phenonetetracarboxylic dianhydride (BTDA)-ODA, and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA)-ODA polyimides were gravimetrically investigated. Water sorption curves were reasonably well fitted by Fickian diffusion despite their morphological heterogeneities in the polyimide thin films. However, the effects of isomeric ODA on the water sorption were quite different depending upon the sort of polyimide. The mutual diffusion coefficient of water and 4,4′ODA based polyimide films varies in the range of 3.0×10^-10 cm²s^-1 to 15.2×10^-10 cm² s^-1, and is in the increasing order: BPDA-4,4′ODA<BTDA-4,4′ODA-PMDA-4,4′ODA<6FD A-4,4′ODA. The water uptake varies from 1.62 wt% to 3.25 wt%, and is in the increasing order: BPDA-4,4′ODA<6FDA-4,4′ODA<PMDA-4,4′ODA< BTDA-4,4′ODA. However, the diffusion coefficient for 3,4′ODA based polyimide films varies in the range of 6.7×10^-10 cm² s^-1 to 8.6×10^-10 cm² s^-1, and is in the increasing order: BPDA-3,4′ODA<6FDA-3,4′ODA-BTDA-3,4′ODA-PMDA- 3,4′ODA. The water uptake varies from 2.02 wt% to 2.98 wt%, and is in the increasing order: 6FDA-3,4′ODA<BPDA-3,4′ODA<BTDA-3,4′ODA< PMDA-3,4′ODA. Polyimides having higher chain order, highly crystalline structure, and smaller mean intermolecular distance revealed relatively lower diffusion coefficients and water uptakes in equilibrium.